The construction and assembly of equipment such as aircraft and automobiles frequently entails drilling holes to accommodate fasteners in structures and fabricating countersinks in such holes to seat the countersunk heads of low-profile fasteners. It is typically important that such holes and countersinks be located accurately and that they be fabricated precisely. In high-volume fabrication operations requiring the fabrication of large numbers of holes and countersinks, it is often important that the time to accomplish such fabrication operations be minimized so as to minimize cost and that such fabrication operations be repeatable.
It is conventional in the construction and assembly of equipment with many sets of holes and countersinks to drill many holes in succession using a drill bit or other cutting tool in a high-speed drill motor and to fabricate countersinks in such holes with a separate countersinking tool after drilling operations have been completed. Conventional fabrication of sets of holes and countersinks thus conventionally requires a separate tool for hole drilling and for countersink cutting and requires two passes over the structure to perform the separate drilling and countersinking operations. Combination drill tools, such as Boeing tool no. TD90F2 manufactured by Carboro Corporation, comprising a drill bit and a countersink cutting surface on a single bit shaft have been developed in response to the need to fabricate holes and countersinks in a single operation.
It is conventional to perform drilling and other fabrication operations with either standard hand-held drill motor units or with power-feed drill motor units. Hand-held drill motor units can be moved quickly from hole to hole, but the full weight of such units must be supported by the operator and forward drill tool pressure must be supplied by the operator. Hand-held units may therefore induce operator fatigue, especially when drilling a large number of holes through hard materials. In contrast, power-feed drill motor units attach firmly to a tooling fixture, which is in turn attached to the structure in which holes are to be fabricated, and forward pressure to the drill tool is supplied by the power-feed unit to enable controlled, repeatable cutting operations and a reduction in operator fatigue.
Hole drill and countersink cutter tools adapted for use with hand-held drill motor units are often incompatible with power-feed drill motor units, so that separate sets of tooling are often required in operations requiring the use of both hand-held and power-feed drill motors.
It is conventional in the construction and assembly of equipment with many features for complex sets of holes and other features to be fabricated with the aid of a tooling fixture, such as a drill plate. If, for example, multiple identical assemblies must be constructed, such as for multiple wing assemblies on an aircraft production line, a durable, reusable drill plate in which a pattern of holes or features has been formed may be used as a template by which holes and features in each assembly may be accurately and repeatably fabricated. The use of a tooling fixture such as a drill plate helps to ensure that all holes in the assembly are precisely located relative to one another.
The minimum spacing between holes which can be formed by the use of a drill plate and conventional drill and countersink cutting tools is typically controlled by the geometry of a nosepiece assembly which engages the tooling plate in an area around or near the drill to align the drill tool with the hole to be drilled. Conventionally, hand-held and power feed drilling motors mate with the tooling plate, in order to align the drill motor prior to commencing drilling operations, by means of a nosepiece assembly comprising radial spring fingers extending through the tooling plate and engaging the tooling plate from the back side of the tooling plate. The geometry of the nosepiece radial spring finger assembly utilized thus dictates how accurately the holes may be drilled and how closely the holes may be spaced conventionally.
As hand-held and power feed units for drilling and countersinking operations are used repeatedly, the accuracy of hole location and hole size may degrade as cutting tools wander or otherwise diverge from the desired drilling axis relative to the tooling plate engagement location. Frequent tool replacement may thus be necessary with conventional drill and countersink tools in applications requiring accurate hole and countersink size and location.
While conventional tools for the fabrication of holes and countersinks in structures provide considerable utility, (1) such tools are typically quite heavy, (2) the nosepiece of such tools is often bulky, thus limiting the minimum spacing between holes which can be accommodated, (3) hole location and hole size accuracy may degrade with repeated heavy use, and (4) separate tools for hand-held and power feed units may be required. Therefore, while a number of drill and countersink fabrication tools have been developed, it is still desirable to develop improved tooling which does not suffer from such limitations inherent to conventional tooling.